The subject invention relates generally to optical waveguides, and more particularly to a method and means which utilize optical waveguides in a matrix configuration for interconnecting multiterminal electronic devices.
Traditionally, wire or printed circuit interconnections have been used for the transmission of data signals between electronic devices (e.g. circuit boards). Such hardwire connections, however, are rather severely limited in data rate handling, usually being limited to less than 1 megabit/second. Furthermore, they tend to suffer from the pick-up of stray RF signals and are subject to other types of electromagnetic radiation induced problems (e.g. EMP). Likewise hardwire data links can also be a source of unwanted RF electromagnetic radiation themselves. Furthermore, since hardwire interconnections are electrically conductive, severe design problems can arise when interconnecting different transistor or IC families (e.g. CMOS, MOS, TTL, etc.) having different logic level voltages.
One answer to this problem is the use of optical fibers as the data signal links. Optical fiber data links have very high bandwidth and neither pick-up nor radiate RF signals. However, there are drawbacks to the use of optical fibers as data transmission links. Interconnecting large numbers of terminals on circuit boards with individual fibers becomes impractical due to the constrained space available for such interconnections. Also, each optical fiber would have to be connected individualy, a slow and time consuming procedure. Thus, assembly would be difficult, leading to high cost and poor reliability.
There have been some attempts to overcome these constraints in the use of optical data links. One approach has been to arrange the optical waveguides in a matrix configuration which would be capable of handling a multitude of data links. This is the approach taken by the subject invention. There have been a number of attempts to utilize the optical waveguide matrix as a means for optically transmitting data on other signals. However, all, for one reason or another, have been deficient in some respect.
U.S. Pat. No. 4,306,765, Winzer et al. discloses one type of optical waveguide matrix. However, the device is limited to seven channels. Although it is conceivable that a device with more channels could be constructed based on the disclosure, the cost of larger capacity devices would become prohibitive since Winzer et al. uses optical fibers or rods as the waveguides. These fibers or rods must be cut and their ends polished at the reflecting joints. Furthermore, Winzer et al. requires a layer of partially-transmissive/partially reflective material which adds to the cost and complexity of the device.
The optical coupler disclosed in U.S. Pat. No. 4,234,969, Singh, utilizes optical waveguides in a matrix configuration to couple data signals into and out of an optical data transmission bus. However, the coupler employs a multitude of optical devices including tapered waveguides, partially reflecting layers, and prisms. The patent discloses a 2.times.2 matrix coupler, but because of the complexity of the arrangement of the waveguides and reflecting surfaces, the device would not be suitable for interconnecting large numbers of data terminals.
U.S. Pat. No. 4,013,000, Kogelnik, discloses an Optical Crossbar Switching Network. This device, although an optical waveguide matrix of sorts, utilizes switchable (grating-type evanescent field) couplers for routing the optical signals between crossing waveguides. Due to the expense of switchable couplers, the switching network disclosed in Kogelnik would not be suitable for low-cost, high-production optical connecting devices.
A major concern in the development of any optical waveguide interconnection matrix is the coupling of the light signal from one waveguide into a crossing waveguide. The current methods for accomplishing this coupling are all rather complex and could be prohibitively expensive when required in large scale. U.S. Pat. Nos. 4,296,995 (Bickel), 4,285,571 (Winzer), 4,176,908 (Wagner), and 3,874,779 (Thiel) all disclose ways and means of coupling optical waveguides. The coupling methods disclosed, however, involve either special processing of the waveguide ends, the insertion of additional optical devices such as prisms and lenses, or the insertion of partially reflective layers of material between the waveguide ends.
In light of the foregoing discussion, it can be aptly concluded that at present there is no simple, inexpensive way to optically interconnect a multitude of data links which is suitable for mass production.